Direct and indirect effects of Littorina littorea (L.) on barnacles growing on mussel beds in the Wadden Sea

On the extensive sedimentary tidal flats of the Wadden Sea, beds of the blue mussel Mytilus edulis represent the only major hard substratum and attachment surface for sessile organisms. On this substratum, the barnacle Semibalanus balanoides is the most frequent epibiont. In summer 1998, it occurred on over 90% of the large mussels (>45 mm shell length) and the dry weight of barnacles reached 65% of mussel dry weight. However, the extent of barnacle overgrowth is not constant and differs widely between years. Periwinkles (Littorina littorea) may reach densities >2000 m^–2 on intertidal mussel beds. Field experiments were conducted to test the effect of periwinkle grazing on barnacle densities. An experimental reduction of grazing and bulldozing pressure by periwinkles resulted in increased recruitment of barnacles, while barnacle numbers decreased with increasing snail density. The highest numbers of barnacles survived in the absence of L. littorea. However, a lack of periwinkle grazing activity also facilitated settlement of ephemeral algae which settled later in the year. Field experiments showed that the growth rate of barnacles decreased in the presence of these ephemeral algae. Thus, L. littorea may reduce initial barnacle settlement, but later may indirectly increase barnacle growth rate by reducing ephemeral algae. It is suggested that periwinkle density may be a key factor in the population dynamics of S. balanoides on intertidal mussel beds in the Wadden Sea.     

The site of settlement indicates commensalism between bluemussel and its epibiont

Summary The site of settlement of barnacles (Balanus improvisus) attached on shells of bluemussels (Mytilus edulis) was mapped from a sample of mussels collected in the Baltic Sea. Most barnacles had settled near the siphonal apertures of the mussel. An experiment was made to measure the disadvantages and advantages that living in close association brings to barnacles and mussels. The barnacles on shells of living mussels were shown to grow significantly faster than those on empty mussel shells. Presence of barnacles had no effects on growth of mussels. The two-species association under study was demonstrated to be a case of commensalism.     

Desiccation,predation, and mussel-barnacle interactions in the northern Gulf of California

Summary Field experiments were conducted in order to determine the potential for desiccation and predation to mediate the effect of mussels (Brachidontes semilaevis) on barnacles (Chthamalus anisopoma) in the highly seasonal northern Gulf of California. We did this by removing both mussels and a common mussel predator (Morula ferruginosa: Gastropoda) and by spraying selected sites with sea water during summertime spring low tides. We also determined the effect of crowding on resistance to desiccation in barnacles, and the effect of barnacles on colonization by mussels. The mussel-barnacle community was not affected by keeping experimental quadrats damp during daytime low tides throughout the summer. Exposure to summertime low tides, however, did affect the survivorship of isolated, but not crowded, barnacles; and barnacle clumps enhanced the recruitment of mussels. Hence crowding in barnacles had a positive effect on both barnacle survivorship and mussel recruitment. Morula had a negative effect on mussel density, and mussels had a negative effect on barnacle density. The effect of Morula on barnacle density was positive, presumably due to its selective removal of mussels. These results suggest an indirect mutualism between barnacles and the gastropod predator, because barnacles attract settlement or enhance the survival of mussels, and the predator reduces the competitive effect of mussels on barnacles.     

Effects of Adult Dreissena polymorpha on Settling Juveniles and Associated Macroinvertebrates

The impact of Dreissena polymorpha settlement on recruitment of juvenile mussels and density of other macroinvertebrates was studied in field experiments using blank concrete blocks and tiles (control), blocks and tiles with attached empty zebra mussel shells, and blocks and tiles with attached living mussels. On blocks, dominant invertebrate taxa showed colonization patterns coinciding with increased habitat complexity owing to zebra mussel settlement or the biodeposition of faeces and pseudofaeces. Adult and especially juvenile zebra mussels preferred blocks with empty shells to blank blocks and blocks with living mussels; this might possibly be caused by a chemical cue that induces gregarious settlement. Lower recruitment on blocks with attached living mussels compared to blocks with only shells could be the consequence of ingestion of larvae by adult mussels and of competition for food. On tiles, the sediments deposited and the organic content of the sediment were investigated. Sedimentation was significantly higher on shell‐only and live‐mussel tiles compared to blank tiles. Organic matter differed significantly between blank and live‐mussel tiles.     

Barnacle larval supply to sheltered rocky shores: a limiting factor?

In northwest Europe, sheltered rocky shores are dominated by fucoid canopy algae and barnacles are rare, although the latter are extremely abundant on exposed shores. The supply of the intertidal barnacle Semibalanus balanoides (L.) to sheltered, fucoid dominated rocky shores was investigated to determine the importance of larval supply in limiting the abundance of adults in shelter. Larval supply was measured at two spatial scales, at the scale of shore (100s of metres), by comparing larval concentrations at exposed and sheltered sites, and at a smaller spatial scale (m), by examining the role of fucoid canopies in limiting supply to the substratum. Replicate plankton trawls were carried out above the intertidal zone at high water at two sheltered sites and nearby exposed headlands. The concentration of S. balanoides cyprid larvae was significantly higher at the sheltered sites on two out of three sampling occasions with up to 14 times greater larvae on one occasion than the nearby exposed site. The effect of the macroalgal canopy on supply to the substratum was assessed in two ways: directly, by pumping water from the substratum in areas with and without Ascophyllum nodosum (L.) Le Jolis, and indirectly by measuring cyprid settlement in a canopy-manipulation experiment. Pumped plankton samples from mid tide level showed that the A. nodosum canopy did not form a barrier to larval supply and may have had a positive effect on larval concentrations at the substratum. Cyprid settlement was assessed in the mid shore A. nodosum and low shore Fucus serratus L. zones to areas with canopy algae (but protected from the sweeping effects of macroalgal fronds) and without canopy. Settlement over three consecutive 24-h periods showed a consistent pattern; settlement was consistently lower beneath the F. serratus canopy than in cleared areas, suggesting that this algal species forms a barrier, limiting supply of cyprid larvae to the substratum.     

Direct and indirect effects of predation,herbivory and surface rugosity on mussel recruitment

Summary The predatory gastropod Nucella lapillus, commonly preys upon the mussel, Mytilus edulis, and is thought to control the distribution and abundance of mussels on the rocky shores of New England, USA. In this study, done in Maine, USA, not only the presence of Nucella lapillus but also the roughness of the experimental surface and the presence of the herbivorous gastropod, Littorina littorea, were manipulated. Four types of surfaces were used as recruitment substrata for mussels: smooth bare granite, aggregations of the barnacle, Semibalanus balanoides, fiberglass resin castings of smooth bare granite and resin castings of aggregations of S. balanoides. To ensure that caged N. lapillus were not starving, barnacles were provided as alternative prey. Experiments showed no detectable effect of N. lapillus on the recruitment of M. edulis. Mussel recruitment was enhanced by surface rugosity and depressed by the activities of L. littorea. Analysis of covariance, using the number of algal species as the covariate, suggested that L. littorea reduced the number of newlyrecruited mussels by removing algae that provided recruitment sites, but no manipulations were done to test this conjecture. It is likely that previous reports of N. lapillus controlling mussel abundance are attributable to N. lapillus preying upon barnacles, which increase surface rugosity and enhance mussel recruitment. Review of literature on feeding preferences of N. lapillus supports this view. When handling times and prey availability are taken into account, Nucella shows a clear preference for barnacles over mussels.     

Factors organizing rocky intertidal communities of New England: Herbivory and predation in sheltered bays

In New England, U.S.A., shores exposed to severe wave action are dominated by the common blue mussel Mytilus edulis L. while moderately protected areas are covered with perennial algae. It is thought that algae are limited by mussels which are a superior competitor. Because the effectiveness of predators is inhibited by wave activity, it is assumed that the rate of predation, which varies across this environmental gradient, accounts for the observed distribution of mussels and algae.Shores along sheltered bays appear to be an exception to this pattern and this study addresses some of the possible causes. In New England bays, mussels and barnacles Semibalanus balanoides (L.) are the most common organisms on the solid surfaces in the lower intertidal zone. Perennial macroalgae, such as Chondrus crispas Stackhouse and Fucus vesiculosus L., are rare. The distribution and abundance of species differs from that on moderately protected shores and is similar to very exposed shores which are dominated by mussels and barnacles.Herbivory by the common periwinkle Littorina littorea (L.) limits the abundance of F. vesiculosus and indirectly affects the success of mussels. During 4 years of experimental manipulations, F. vesiculosus rarely recruited in the presence of periwinkles but dominated experimental surfaces if periwinkles were excluded. When experimental surfaces with F. vesiculosus, which had been protected from herbivory for > 1 year, were exposed to natural conditions, herbivores cleared most of the surfaces within several months. Recruitment by barnacles and mussels was higher when periwinkles were excluded. However, the effect of periwinkles on mussels was indirect; the snails reduced barnacle success and thus reduced mussel recruitment which was enhanced by the surface irregularities provided by barnacles.The occurrence of mussels in sheltered bays is not due to a lack of predators. Predators were commonly seen at all sites. Most mussels on experimental surfaces were removed <4 wk when surfaces were exposed to natural levels of predation. Experiments do not provide an explanation for the occurrence of mussels, although the enhancement of mussel recruitment by barnacles suggests that the availability of settlement sites may be important.     

Discrimination at settlement in barnacles: Laboratory and field experiments on settlement behaviour in response to settlement‐inducing protein complexes

A major driving force to mechanistic studies of barnacle gregarious settlement is to contribute to an understanding of observed patterns of settlement in nature. In particular, how cyprids perceive adult conspecifics and how they discriminate between conspecific and allospecific barnacles are questions which have taxed researchers for nearly 50 years. The putative, active component of adult barnacles to which the cyprids respond has long been known to be a glycoprotein, referred to here as the settlement‐inducing protein complex (SIPC). The present study examines the discriminatory abilities of laboratory‐reared Balanus amphitrite and wild Semibalanus balanoides cyprids at settlement. Using a recently developed nitrocellulose membrane‐choice settlement assay, laboratory studies revealed that both species settled at a significantly higher rate on regions of membrane on which crude conspecific SIPC had been adsorbed compared to untreated regions. Moreover, when offered a choice between conspecific and allospecific SIPC, a trend to greater settlement on the conspecific regions was observed. The membrane assay was also evaluated in field trials using real‐time video footage of cyprid searching behaviour. Of 211 S. balanoides cyprids recorded during exploratory behaviour, only one settled. Exploratory behaviour was, however, clearly associated with regions of the membrane treated with either conspecific or allospecific (B. Amphitrite) SIPC compared to untreated regions. These results are generally in accord with previous reports on the discriminatory abilities of barnacle cyprids and suggest that the membrane assay may be usefully applied to field studies of settlement behaviour.     

Bewuchsuntersuchungen auf Natursteinsubstraten im Gezeitenbereich des Nordsylter Wattenmeeres: Sessile und hemisessile Tiere

Six different types of test substrates, arranged in order of texture from smooth (Solnhofen limestone, Bunter sandstone, and basalt) to rough surfaces (Middle Triassic limestone, granite, and basaltic lava), were exposed in tidal zone of the wadden sea near the harbour of List (Island of Sylt, North Sea). The test substrates were fixed to panels at the midtide to high-water level, the midtide to low-water level, and 75 cm below the latter (sublittoral level). Animal settlement was primarily influenced by abiotic factors at the two higher levels. In the sublittoral zone, however, influences of biotic factors (competitors and predators) predominated. Therefore, the physical quality of the chosen substrates more decisively affected the growth of settling animals above the midtide to low-water mark than in the deeper zone. At the midtide to high-water levelBalanus balanoides only settled on the rough surface of the Middle Triassic limestone and in the troughs of the Bunter sandstone; barnacles attached to the even surface of the latter, were destroyed by wave beating. They died on the rough surface of the dark-coloured granite, when this stone was warmed during low-water. At the midtide to low-water level, the barnacles survived best on the rough surface of the Middle Triassic limestone and the granite. Only the larvae ofB. crenatus andB. improvisus preferred to settle on the even surface of the Bunter sandstone and the basalt; but there they died from wave beating or desiccation. The surface of the basaltic lava, formed by sharp-edged pores, was unsuitable for settling of barnacles. Colonies of Hydrozoa covered each substrate with a somewhat rough surface structure, even the basaltic lava. At the sublittoral level, differences in settling between the single substrates disappeared more and more. Nevertheless, the three species of barnacles showed the same preferences in settling, as they did at the higher levels. In August,Asterias rubens destroyed all barnacles and thus restricted the lower limit of barnacle settlement at the low-water mark. The distribution of epibiotic organisms is dependent upon the density of their living substrates, directly attached to the stone surfaces. During the short time of their growth, hemisessile young,Mytilus edulis settled on thready forms like algae, or on raised areas like the top of barnacle shells. Therefore, young mussels could be found on stones, that already carried a compact cover ofEnteromorpha sp. or a dense settlement of adult barnacles. The polychaetePolydora ciliata rarely burrowed directly into stony substrates (Middle Triassic limestone, Solnhofen limestone). It settled primarily between barnacle shells where it was sheltered from wave beating and at the same time profited from the current produced by the filter-feeding organs of the barnacles. The density of this polychaete was directly proportional to the density of the barnacles. AfterA. rubens had destroyed the barnacles in the sublittoral zone,P. ciliata disappeared too. At the low-water mark, however, theP. ciliata population between living and active barnacles increased. Hence, the lower limit ofP. ciliata — as those of barnacles and mussels — was fixed by this predator.

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Herrn Professor W. E. Ankel zur Vollendung des 80. Lebensjahres in Dankbarkeit gewidmet.     

Modeling variation in interaction strength between barnacles and fucoids

The strength by which species interact can vary throughout their ontogeny, as environments vary in space and time, and with the density of their populations. Characterizing strengths of interaction in situ for even a small number of species is logistically difficult and may apply only to those conditions under which the estimates were derived. We sought to combine data from field experiments estimating interaction strength of life stages of the barnacle, Semibalanus balanoides, on germlings of Ascophyllum nodosum, with a model that explored the consequences of variability at per capita and per population levels to the abundance of year-old algal recruits. We further simulated how this interaction affected fucoid germling abundance as the timing of their respective settlements varied relative to one another, as occurs regionally across the Gulf of Maine, USA. Juvenile S. balanoides have a weak estimated per capita effect on germlings. Germling populations are sensitive to variation in per capita effects of juvenile barnacles because of the typically large population sizes of the latter. However, high mortality of juvenile barnacles weakens the population interaction strength over time. Adult barnacles probably weakly facilitate fucoid germlings, but greater survival of adults sustains the strength of that interaction at the population level. Germling abundance is positively associated with densities of adult barnacles and negatively associated with that of juvenile barnacles. Metamorphosing cyprid larvae have the strongest per capita effect on germling abundance, but the interaction between the two stages is so short-lived that germling abundance is altered little. Variation in the timing of barnacle and A. nodosum settlement relative to one another had very little influence on the abundance of yearling germlings. Interactions between barnacles and germlings may influence the demographic structure of A. nodosum populations and the persistence of fucoid-dominated communities on sheltered rocky shores in New England. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of oil shale on intertidal organisms: Effect of oil shale extract on settlement of the barnacle Balanus balanoides (L.)

As part of a study to investigate the effect of oil seeps on intertidal organisms, oil extracts of Blackstone oil shale from Kimmeridge on the Dorset coast were used in laboratory experiments to test their effect on the settlement of the barnacle Balanus balanoides (L.). Thin films of oil extract painted on the surface of pits in slate panels had no effect on cyprid settlement when applied up to a surface density of 2.8 g · m^?2, representing a thickness of 3.3 μm. Larger surface densities of oil stimulated cyprids to settle in far greater numbers than on unoiled panels. The maximum effect was obtained at a surface density of between 14.0 and 56.0 g · m ^?2, representing a thickness of 16.5 μm and 66.0 μm. With higher concentration of oil in the pits, stimulation to settle was reduced although cyprid settlement was still encouraged at a surface density of oil of 112g · m^?2 or 132 μm thickness.The unfractionated crude oil shale extract was a less powerful stimulus for barnacle settlement than a partially purified solution of the integumental protein arthropodin, another strong settlement inducer for barnacle cyprids.     

Age-dependent zonation of the periwinkle Littorina littorea (L.) in the Wadden Sea

On sedimentary tidal flats near the island of Sylt (German Bight, North Sea) abundance and size distribution of periwinkles, Littorina littorea L., were studied in low intertidal and in shallow and deep subtidal mussel beds (Mytilus edulis L.). In low intertidal mussel beds, surveys revealed that high densities (1,369±571 m^–2) of juvenile snails (≤13 mm) were positively correlated with strong barnacle epigrowth (Semibalanus balanoides L. and Balanus crenatus Bruguière) on mussels. A subsequent field experiment showed that recruitment of L. littorea was restricted to the intertidal zone. Abundances of periwinkles (213±114 m^–2) and barnacles abruptly decreased in the adjacent shallow subtidal zone, which served as a habitat for older snails (>13 mm). L. littorea was completely absent from disjunct deep (5 m) subtidal mussel beds. Snail abundance varied seasonally with maxima of >4,000 m^–2 in low intertidal mussel beds in October and minima in July, just before the onset of new recruitment. I suggest that the presence of cracks and crevices among the dense barnacle overgrowth in intertidal mussel beds favoured recruitment and survival of juvenile snails. Larger (older) specimens are assumed to actively migrate to the less favourable adjacent subtidal. Therefore, intertidal mussel beds are considered as nurseries for the population of L. littorea in the Wadden Sea. Received in revised form: 25 September 2000 Electronic Publication     

Adult Prey Neutralizes Predator Nonconsumptive Limitation of Prey Recruitment

Recent studies have shown that predator chemical cues can limit prey demographic rates such as recruitment. For instance, barnacle pelagic larvae reduce settlement where predatory dogwhelk cues are detected, thereby limiting benthic recruitment. However, adult barnacles attract conspecific larvae through chemical and visual cues, aiding larvae to find suitable habitat for development. Thus, we tested the hypothesis that the presence of adult barnacles (Semibalanus balanoides) can neutralize dogwhelk (Nucella lapillus) nonconsumptive effects on barnacle recruitment. We did a field experiment in Atlantic Canada during the 2012 and 2013 barnacle recruitment seasons (May–June). We manipulated the presence of dogwhelks (without allowing them to physically contact barnacles) and adult barnacles in cages established in rocky intertidal habitats. At the end of both recruitment seasons, we measured barnacle recruit density on tiles kept inside the cages. Without adult barnacles, the nearby presence of dogwhelks limited barnacle recruitment by 51%. However, the presence of adult barnacles increased barnacle recruitment by 44% and neutralized dogwhelk nonconsumptive effects on barnacle recruitment, as recruit density was unaffected by dogwhelk presence. For species from several invertebrate phyla, benthic adult organisms attract conspecific pelagic larvae. Thus, adult prey might commonly constitute a key factor preventing negative predator nonconsumptive effects on prey recruitment.     

Surface wettability as a determinant in the settlement of the barnacle Balanus Improvisus (DARWIN)

Several studies have shown that the initial surface wettability, is of importance in the settlement of macrofouling larvae such as barnacles, bryozoans and hydroids in the field as well as in laboratory assays. In this study we present results from laboratory assays using hydrophilic and hydrophobic polystyrene (PS) and cyprid larvae of Balanus improvisus (Darwin). The results obtained differ markedly from those reported for the barnacle Balanus amphitrite (Darwin), where a high surface wettability seemed to be preferred for settlement. Our results show that a surface with intermediary wettability (hydrophilic PS) reduced settlement by 38% as compared to surfaces of low wettability (hydrophobic PS) during an 8-day period. During the experiment, the wettability in the hydrophilic PS dishes was not significantly changed as measured by advancing contact angle with mQ water. Over an 8-day period wettability of the hydrophobic PS dishes approached that of the hydrophilic PS surfaces. We further conducted experiments with highly hydrophilic and highly hydrophobic methylsilane-treated glass surfaces with known chemistry. In this experiment, the settlement of cyprid larvae was completely inhibited by the high wettability surfaces. Contact angle measurements revealed that the wettability during the length of the experiment of the hydrophilic glass surfaces was not significantly altered. We conclude by these experiments that even an intermediate wettability can significantly affect the overall settlement success of the barnacle B. improvisus. The mechanism by which the settlement is impeded might be biologically mediated through the recognition by cyprid larvae of the molecular composition of the surface when the cyprid reverts to the settlement phase, i.e. when swimming behaviour is abandoned in favour of surface exploration, or it is mediated by physicochemical forces acting between the surface and the larval body or the larval antennules.     

Effect of ultrasound on cyprids and juvenile barnacles

Settlement inhibition of barnacle (Amphibalanus amphitrite) cypris larvae resulting from exposure to ultrasound was measured at three frequencies (23, 63, and 102 kHz), applied at three acoustic pressure levels (9, 15, and 22 kPa) for exposure times of 30, 150, and 300 s. The lowest settlement was observed for 23 kHz, which also induced the highest cyprid mortality. Cyprid settlement following exposure to 23 kHz at 22 kPa for 30 s was reduced by a factor of two. Observing surface exploration by the cyprids revealed an altered behaviour following exposure to ultrasound: step length was increased, while step duration, walking pace, and the fraction of cyprids exploring the surface were significantly reduced with respect to control cyprids. The basal area of juvenile barnacles, metamorphosed from ultrasound-treated cyprids was initially smaller than unexposed individuals, but normalised over two weeks' growth. Thus, ultrasound exposure effectively reduced cyprid settlement, yet metamorphosed barnacles grew normally.     

Topographically generated fronts, very nearshore oceanography and the distribution and settlement of mussel larvae and barnacle cyprids

Flow patterns adjacent to shore may prevent or aid shorewardmigration of benthic invertebrate larvae. We hypothesized thata front at the mouth of Sunset Bay, Oregon, prevents shorewarddispersal of larvae, significantly altering settlement of mussellarvae and barnacle cyprids. Settlement was measured at threesets of moorings (three moorings per site) distributed acrossthe front at Sunset Bay. From 6 July to 4 September 2000, sampleswere collected roughly every other day. Concurrently, we madevertical zooplankton tows adjacent to each mooring site andcollected physical oceanographic data. During upwelling-favorablewinds, the front was always present at the bay mouth, separatingsignificantly cooler, saltier and denser offshore water fromthat within the bay. During downwelling winds, the front brokedown and we found no significant difference in the surface physicaloceanographic parameters across the bay mouth. During upwelling,the concentration of mussel larvae was higher seaward of thefront than landward, but there was no significant differencein concentration during downwelling, suggesting that the frontmay act as a barrier to the shoreward dispersal of mussels.Mussel settlement was too low and sporadic to allow statisticalanalysis. There was no difference in cyprid concentrations acrossthe bay mouth whether the front was present or not. Cyprid settlementwas, however, nearly an order of magnitude lower at mooringsseaward of the front than at those landward. A significant cross-correlationwas found between settlement at the offshore mooring and tidalrange (r = 0.464, lag = 0 days) and between settlement at themid and inner moorings and downwelling winds (r = 0.532 midbay, r = 0.532 inner bay, lag = 0 days). Seaward of the front,settlement varied with tidal range, while landward of the front,most settlement occurred as brief pulses during downwellingwinds, periods when the front was not present. We found largedifferences in the distribution of cyprids, and mussel larvaeand cyprid settlement relative to the front; larval distributionsand settlement varied with upwelling versus downwelling windsand was due to differences in the very nearshore (i.e. within100–1000 m of shore) coastal oceanography.     

Stylochus tauricus,a predator of the barnacle Balanus improvisus in the Black Sea

The flatworm Stylochus tauricus Jacubova has been found associated with the barnacle Balanus improvisus Darwin, on which it feeds. The predation rate (the number of barnacles eaten by one polyclad in a month) ranges between 5–10. Inside the empty shells of B. improvisus some egg-plates of S. tauricus were observed. Pelagic Götte's larvae aged 2–3 days possess 4 lobes while those aged 7–8 days have 5 lobes. Flatworms can prey on the young of another species Balanus eburneus Gould, whereas predation on the mussels Mytilus galloprovincialis Lam. is rare. There is a direct correlation between predator abundance and prey ingested.     

Survivorship of juvenile barnacles and mussels: spatial dependence and the origin of alternative communities

Mussels, barnacles, and rockweeds often form a distinct mosaic of patches on rocky intertidal shores, and it has been suggested that these communities may represent alternative community states. One way that alternative community states can arise is if early successional events are scale-dependent, but it is not known if juvenile survivorships of mussels and barnacles are, in fact, scale-dependent. Scale-dependence of barnacles (Semibalanus balanoides (L.)) and mussels (Mytilus edulis L.) was tested in the Gulf of Maine, USA. In winter 1997, clearings of 1, 2, 4 and 8 m in diameter and uncleared controls were made in stands of the rockweed Ascophyllum nodosum (L.) Le Jolis at 12 sites spread evenly across four bays on Swan's Island, ME. Summer and fall-winter survivorship of barnacles, which recruited in spring 1997, were estimated by tracking the 1997 cohort until late winter 1998. Survivorship of mussels was estimated from following the fate of transplanted juveniles over 4 days in late August 1997. Both barnacles and mussels showed better survival in 4 and 8 m clearings than in small clearings and controls. There was also significant variation in survivorship among sites. Densities of gastropods in the clearings did not reflect survivorship patterns of barnacles and mussels. Barnacle survivorship increased in fall and winter, and in large clearings was comparable to survivorship in barnacle-dominated habitats. Mussel survivorship was low in all clearing sizes suggesting that mussel beds develop slowly.     

Interactions of Patella and macroalgae with settling Semibalanus balanoides (L.)

Biological interactions affecting densities of settling and newly-settled Semibalanus balanoides (L.) have been investigated by manipulative field experiments on the Isle of Man.The effects of sweeping by fucoid clumps of different species and Patella browsing have been compared on moderately-exposed shores. Patella allowed barnacle settlement by preventing growth of competing green algae, but reduced post-settlement densities. Small clumps of Fucus spiralis L., F. vesiculosus L, and F. serratus L. all reduced settlement considerably more so than limpets. F. serratus had the greatest sweeping effect.Interactions between macroalgae and Semibalanus balanoides have been investigated at all levels on sheltered shores and low down on more exposed shores. In the Fucus spiralis and F. vesiculosus zones, post-settlement numbers were higher than in adjacent areas where the canopy was removed. Barnacles did not settle readily in the Ascophyllum zone in either experimental or control areas. Settlement occurred in the upper part of the Fucus serratus zone in experimental areas where the canopy was removed but not in control areas. No settlement occurred in either treatment or control areas lower in the F. serratus zone. At all levels on the shore fucoid canopies seemed to reduce cyprid settlement, but the effect was greatest amongst F. serratus where there was total prevention. High on the shore the effect of enhanced post-settlement survival under the canopy outweighs reduction of cyprid settlement thus there are greater numbers in the controls. Competition with red algal turfs was shown to set the lower limit of the barnacle zone on a vertical pier face.     

Settlement Dynamics of the Encrusting Epibenthic Macrofauna in Two Creeks of the Caeté Mangrove Estuary (North Brazil)

The epibenthic encrusting fauna of 2 creeks of the Caeté mangrove estuary, northern Brazil, was studied over a 13 month period using collectors fixed at 2.5 and 3.5 m above the creek bottom and in which upper and lower sides of ceramic and wooden panels were used as settlement substrates. The number of individuals of the most abundant organisms (barnacles, oysters and mussels) settling per panel was determined each month, for each substrate type, panel orientation and height above creek bottom. The barnacle, Fistulobalanus citerosum has a peak settlement period during the wet season whereas both peaks in the numbers of settlers of the oyster Crassostrea rhizophorae were recorded during the dry season and such discrete temporal patterns in settlement have also been observed for barnacles and oysters in other mangroves and estuaries. In contrast to other studies, settlement of the mussel Mytella falcata was generally low during the study period and may be related to over-exploitation of stocks in the region. Overall, settler density was usually greater on the underside of ceramic panels close to the creek bottom, similar to results of other studies of epibenthic settlement in diverse habitats.